This invention relates to the field of article counting and more particularly to the counting of bottles, jars, cans, containers and similar objects being transported along a conveyor. Counting of such articles is complicated by the fact that they tend to back up and reverse direction on the conveyor, so that individual articles become indistinguishable to commonly used sensors. The prior art does include arrangements for counting overlapped sheets, newspaper sections, signatures and the like with the aid of specially positioned ultrasonic transmitters and receivers. However, the positioning of the transmitters and receivers is peculiar to the geometry of overlapped sheet-like articles. Such counting systems are not entirely suitable for counting irregularly shaped and variously spaced articles traveling in an upright orientation along a conveyor. An example of such a counting system appears in Duss U.S. Pat. No. 5,005,192.
The prior art also includes counting systems having inductive proximity sensors which may be placed in pairs on the same side of a pass line or on opposite sides thereof. The two sensors are offset for performing a quadrature count. These sensors are suitable only for counting metallic articles. Also, whenever the article size is changed the sensors must be realigned.
Yet other prior art uses pairs of optical sensors which are laterally separated by a distance equal to half the diameter of articles being sensed, so that a given article is sensed by both sensors sequentially and at different times before another article is sensed by either sensor. Again, the sensors must be realigned upon changes of article size.
It is therefore seen that there is a need for an improved apparatus and method for counting progressions of variously positioned articles of arbitrary construction which may start, stop and reverse their direction of movement.